1. Field of the Invention
The present invention relates to a laminated electronic component and a method for manufacturing the laminated electronic component, and more particularly, to a laminated electronic component including a plated external terminal electrode plated directly on the laminated electronic component so as to be electrically connected to a plurality of internal electrodes, and a method for manufacturing the laminated electronic component.
2. Description of the Related Art
As shown in FIG. 5, a laminated electronic component 101 defining a laminated ceramic capacitor is typically provided with a component main body 105 which includes a stacked structure including a plurality of stacked insulator layers 102 made of, for example, a dielectric ceramic and a plurality of layered internal electrodes 103 and 104 disposed along the interfaces between the insulator layers 102. The respective ends of the plurality of internal electrodes 103 and the plurality of internal electrodes 104 are respectively exposed at opposite end surfaces 106 and 107 of the component main body 105, and external terminal electrodes 108 and 109 are arranged so as to electrically connect the respective ends of the internal electrodes 103 to each other and electrically connect the respective ends of the internal electrodes 104 to each other.
For the formation of the external terminal electrodes 108 and 109, typically, a metal paste including a metal component and a glass component is applied onto the end surfaces 106 and 107 of the component main body 105, and then fired, thereby forming a paste electrode layer 110. Next, a first plating layer 111 including, for example, nickel as its main component is formed on the paste electrode layer 110, and a second plating layer 112 including, for example, tin or gold as its main component is formed on the first plating layer 112. More specifically, each of the external terminal electrodes 108 and 109 includes a three-layer structure of the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external terminal electrodes 108 and 109 are required to have favorable solderability when the laminated electronic component 101 is mounted on a substrate via solder. At the same time, the external terminal electrode 108 is required to have the function of electrically connecting the plurality of internal electrodes 103 to each other, which are electrically insulated from each other, and the external terminal electrode 109 is required to have the function of electrically connecting the plurality of internal electrodes 104 to each other, which are electrically insulated from each other. The second plating layers 112 ensure the solderability and the paste electrode layers 110 electrically connect the internal electrodes 103 to each other and the internal electrodes 104 to each other. The first plating layers 111 prevent solder erosion in the solder joint.
However, the paste electrode layer 110 has a large thickness, from several tens of μm to several hundreds of μm. Therefore, in order to limit the dimensions of the laminated electronic component 101 to certain specifications, the effective volume for providing a capacitance must be reduced because the thickness and volume of the paste electrode layers 110. On the other hand, the plating layers 111 and 112 have a thickness of only several μm. Thus, if the external terminal electrodes 108 and 109 can be defined by only the first plating layers 111 and the second plating layers 112, the effective volume for providing the capacitance can be increased.
For example, Japanese Unexamined Patent Publication No. 2004-146401 discloses a method in which a conductive paste is applied along at least ridge sections of end surfaces of a component main body in the direction of stacking internal electrodes so as to come into contact with leading sections of the internal electrodes, and the conductive paste is fired or thermally cured to form a conductive paste. Further, the end surfaces of the component main body are subjected to electroplating, thereby forming an electroplating film so as to be connected to the conductive film on the ridge sections described above. According to this method, the thickness of the external terminal electrodes at the end surfaces can be reduced.
In addition, Japanese Unexamined Patent Publication No. 63-169014 discloses a method in which a conductive metal film is deposited by electroless plating on the entire sidewall surface of a component main body, at which internal electrodes are exposed, so as to short circuit the internal electrodes exposed at the sidewall surface.
However, in the methods for forming external terminal electrodes as described in Japanese Unexamined Patent Publications No. 2004-146401 and No. 63-169014, plating is performed directly on the ends at which the internal electrodes are exposed. Thus, a plating solution is likely to enter the component main body along the interfaces between the internal electrodes and the insulator layers and may erode the ceramic defining the insulator layers and the internal electrodes, thereby causing structural defects. Furthermore, this results in defects in terms of reliability, such as degraded load characteristics against humidity for the laminated electronic component.
In particular, when tin or gold plating is to be applied, the problems described above are more likely to be caused because a tin or gold plating solution generally contains a highly corrosive complexing agent.
In order to solve the problems described above, for example, the International Publication No. WO2007/119281 discloses providing a water repellent agent on end surfaces of a component main body at which respective ends of internal electrodes are exposed, in order to fill the gaps at the interfaces between insulator layers and the internal electrodes with this water repellent agent, and then forming plating layers as bases of external terminal electrodes onto the end surfaces. Such a water repellent agent improves the lifetime characteristics in a load test against humidity.
However, the technique described in International Publication No. WO2007/119281 has the following problems.
The water repellent agent is likely to adhere to the ceramic sections defining the insulator layers, rather than the metal sections defining the internal electrodes. If the distance between the internal electrodes is large (that is, when the insulator layers are thick and when the number of stacked internal electrodes is small), most of the end surfaces at which the respective ends of the internal electrodes are exposed will be covered with the water repellent agent, which decreases the ability to deposit plating onto the end surfaces at which the internal electrodes are exposed.
In addition, in order to improve the fixing strength of the external terminal electrodes to the component main body, a heat treatment may be performed at a temperature of about 800° C. or more after the formation of the plating layers as bases. However, such a heat treatment will cause the water repellent agent to disappear.
It is to be noted that, for example, Japanese Unexamined Patent Publication No. 2002-289465 discloses providing a water repellent agent before a plating process when forming paste electrode layers by firing and then performing plating as in the prior art described with reference to FIG. 5, rather than forming external terminal electrodes substantially only by plating. The paste electrode layers formed by firing are not only formed on end surfaces of a component main body in the shape of a rectangular parallelepiped, at which respective ends of internal electrodes are exposed, but also formed so that the end edges of the paste electrode layers are located on the principal surfaces and side surfaces adjacent to the end surfaces.
However, the technique described in Japanese Unexamined Patent Publication No. 2002-289465 above encounters the following problem. Moisture is likely to enter from the gaps between the end edges of the paste electrode layers formed by firing and the component main body because segregation of a glass component is likely to occur in this section of the gaps and the glass is easily dissolved by the plating solution even if the glass is coated with the water repellent agent.